1. Field of the Invention
The present invention relates to an organic electroluminescence (OEL) pixel with high color saturation and high luminescent efficiency, an organic electroluminescence device comprising OEL pixels, and a manufacturing method thereof.
2. Descriptions of the Related Art
With the advantages of self-emission, high luminescent efficiency, high contrast ratio, and ultra wide viewing angle, the organic electroluminescence display (OELD) is increasingly becoming a focus of research in the electronic display field. The OELD can be divided into two categories: the active matrix organic electroluminescence display (AMOELD) and the passive matrix organic electroluminescence display (PMOELD).
Since the OELD technology eliminates the need of backlit modules and features self-emission capability, higher contrast ratio, lower power consumption, wider viewing, slimmer thickness as well as a higher response speed compared to liquid crystal display (LCD) technology, it is better suited for electronic products for future generations. It is therefore considered as one of the most promising display technologies of the future.
As shown in FIG. 1, an OEL device 1 in a conventional AMOELD comprises a plurality of OEL pixels 1r, 1g, 1b, a substrate 11, an active matrix circuitry layer 12, a plurality of transparent lower electrodes 13r, 13g, 13b, a pixel insulation layer 15, an organic emitting layer 17, and an upper electrode 19. The OEL pixels 1r, 1g, 1b are configured to emit red light, green light, and blue light, respectively. The substrate 11 further comprises a plurality of thin film transistors (TFTs) 111, 113, 115 and a plurality of signal lines 116. The TFT 111 is configured to control the OEL pixel 1r in the OEL device 1 to emit red light, the TFT 113 is configured to control the OEL pixel 1g in the OEL device 1 to emit green light, and the TFT 115 is configured to control the OEL pixel 1b in the OEL device 1 to emit blue light. The pixel insulation layer 15 is configured to define the emitting area of respective OEL pixels 1r, 1g, 1b. The signal lines 116 are configured to transfer signals.
In order for the aforesaid OEL device 1 to emit red light, the TFT 111 is turned on to energize the lower electrode 13r, thus allowing the OEL pixel 1r to emit red light. At the same time, the TFTs 113 and 115 are turned off, so as not to allow the OEL pixels 1g and 1b to emit light. As a result, the OEL device 1 only emits red light.
However, in this type of conventional bottom-emission AMOELD, constraints imposed by the materials used often leads to insufficient color saturation in the OEL device 1. Therefore, in the conventional technologies, microcavity structures are further fabricated to improve the luminescent efficiency and color saturation of the OEL pixels 1r, 1g, 1b. As shown in FIG. 2, the OEL device 2 is similar to the OEL device 1 in most of its structure, and comprises a plurality of OEL pixels 2r, 2g, 2b, a substrate 21, an active matrix circuitry layer 22, a plurality of transparent lower electrodes 23r, 23g, 23b, a pixel insulation layer 25, an organic emitting layer 27, and an upper electrode 29. The OEL pixels 2r, 2g, 2b are configured to emit red light, green light, and blue light, respectively. The substrate 21 further comprises a plurality of TFTs 211, 213, 215 and a plurality of signal lines 216.
In conventional technology as shown in FIG. 2, in order to fabricate OELDs with microcavity structures, a photo-etching process is utilized to form patterned semi-trans-flective metal electrodes 24r, 24g, 24b on the transparent lower electrodes 23r, 23g, 23b. The pixel insulation layer 25 is then formed thereon to define an emitting area for the pixel. However, this requires an additional photo-etching process in the existing TFT process, which adds to the manufacturing costs. Moreover, surfaces of the semi-trans-flective metal electrodes exposed in the photo-etching process may suffer from at least one of oxidation, increased surface roughness, residue of conductive substances, and/or residue from organic substances, all which will have adverse effect on the properties of the device (e.g., incurrence of short circuits, variation of electrical property, and variation of operation voltage).
In addition to the need of forming patterned semi-trans-flective metal electrodes on the transparent lower electrodes 23r, 23g, 23b, the microcavity structure described above also requires an organic film layer with appropriate thickness in the OEL device 2. The thickness of the organic film layer must be selected appropriately in order to improve the color saturation and luminescence efficiency of the OEL device 2. A thinner organic film layer (i.e. the organic emitting layer 27) will undoubtedly endow the OEL device 2 with better luminescent efficiency and color saturation. However, due to the uneven surface of the transparent lower electrodes 23r, 23g, 23b and/or the semi-trans-flective metal electrodes 24r, 24g, 24b (e.g., protrusions on the semi-trans-flective metal electrodes 24g in FIG. 2), an unduly thin organic film layer tends to cause a current leakage or even a short circuit between the upper electrodes 29 and the transparent lower electrodes 23r, 23g, 23b or the upper electrodes 29 and the semi-trans-flective metal electrodes 24r, 24g, 24b in the OEL device 2. On the other hand, if the organic film layer has its thickness increased in order to eliminate the aforesaid current leakage phenomenon in the OEL device 2, variation of its luminescent efficiency and color saturation will be increased due to an uneven thickness of the organic film layer.
Accordingly, an effort still has to be made in this field to enhance the luminescent efficiency and color saturation of the OEL devices in OELDs without introducing any additional process, and without modifying the existing manufacturing process and yield thereof.